1. Field of Invention
The present invention relates to an implant for performing interbody fusion within a human spine, inserters for such an implant, and associated methodology. More specifically, the implant aspect of the present invention involves an implant formed in situ from at least two separate but lockable members (a base member and a closure member), wherein: (a) the base member may be implanted into an interbody space first, after which the end plates may be finally prepared and the base member packed with fusion promoting substances before engaging and locking the closure member; and (b) the closure member provides structural support for the adjacent vertebral bodies (along with the base member) and may be selected after implantation of the base member having a specific length, width, height, taper, etc. . . . to ensure an optimal sizing of the implant for desired restoration of disc height, coronal taper, sagittal taper, etc. . . . .
2. Discussion of the Prior Art
The human spinal column is made up of a series of vertebral bodies with intervertebral discs disposed there between, which collectively provide support and structure for the body while allowing motion and flexibility, as well as protection for the spinal cord running through the spinal column and associated nerve roots which exit the spinal column. Various traumatic events and/or degenerative conditions may result in undesirable motion or change in disc height, both of which may cause chronic pain for the affected individual. The degree and treatment of pain varies by the individual but in many instances the pain can be disabling and uncontrollable by conservative means, leaving surgery as the only viable option. In many cases, the primary surgical treatment involves interbody fusion, wherein an implant is introduced into the disc space to restore the disc height and establish a bony bridge between the adjacent vertebral bodies with the goal of eliminating or at least reducing the pain of the affected individual.
To enable the introduction of an interbody fusion implant, the surgeon must perform the following steps to create a suitable environment for post-operative fusion: (a) surgical access to the affected disc space; (b) an annulotomy to gain access into the interior of the affected disc; (c) an initial or preliminary discectomy to remove some or all of the nucleus pulposus within the affected disc; and (d) final endplate preparation to remove the cartilaginous disc material to expose the underlying bony endplates of the adjacent vertebral bodies (preferably without violating the bony endplates). Final endplate preparation is a critical step in implant placement and achieving a solid fusion. It is required to remove all the cartilaginous disc material while not violating the bony end plate. Not removing the cartilaginous end plate can result in a delayed bony growth or incomplete bony growth, while fracturing the bony end plate can result in a fracture of the vertebral body and post-operative settling of the implant with concomitant loss of disc height and/or vertebral body alignment. Repetitive insertion of instruments into the disc space during the process of final endplate preparation can result in possible injury to the neural and vascular structures surrounding the disc space if the instruments are inadvertently passed or extended outside the disc space by the surgeon.
To help facilitate fusion, the implants preferably include one or more “fusion windows,” that is, apertures extending from the superior surface to the inferior surface of the implant to allow bone to form through the implant to ensure a solid and robust fusion. To further facilitate fusion, these apertures may be filled with fusion promoting materials including but not limited to cancellous autograft bone, allograft bone, demineralized bone matrix (DBM), porous synthetic bone graft substitute, bone morphogenic protein (BMP), mesenchymal stem cells and/or combinations thereof and/or functional equivalents. Such materials are traditionally introduced into the implant before the implant is introduction into the disc space. Based on the oftentimes high amount of force required to be applied to the corresponding insertion tools, such fusion promoting substances can become loosened or dislodged during the introduction of the implant, which can in certain instances increase the amount of time required to achieve fusion.
Implants can be introduced into the interbody space in one of several known approaches or directions to the spine, including posterior (from the back), anterior (from the front), and lateral (from the side). Before 2003, interbody fusion via a lateral approach was uncommon because of the inability to safely pass through the psoas muscle, which flanks either side of the lumbar spine and includes the lumbar plexus. Lateral access surgery became safe and reproducible with the advent of the NeuroVision® system by NuVasive, Inc., which automatically detects the presence of nerves in the psoas muscle via surgeon-directed neurophysiology in combination with minimally disruptive access instrumentation (e.g. dilators, retractor, etc. . . . ) to aid the surgeon in avoiding nerves while establishing an operative corridor from a lateral approach.
The present invention addresses the need for additional interbody implant options, inserters, and techniques for use in lateral access surgery.